P-acylaminophenyl



Patented Jan. 24, 1961 since it was found that increasing the molecular size of the N-substituent actually increases the toxicity and re N-lt-(p-ACYLAMWOPHENYL) EHIYLl-tt-PHENYL- 5582etrifxitiiiiiiniifgwiitt if gist 3, 553%:

5 half the analgesic activity of meperidine).

Surprisingly enough, the new compounds, N-[B-(p- John Weijlard and Karl Pfister HI, Westfield, N.J., asaminophenyl)ethyl]-4-phenyl 4-carboethoxypiperidine, its Q Merck & y, 3 P N-acyl derivatives, and salts, have been found to possess l'atltm Of New Jersey satisfactory analgesic activity at levels at which meper- No Drawing Original application May 26, 1955v Sen 10 idine possesses no analgesic activity whatsoever; at com- 5 Divided and this application No 14, parable analgesic activity, the tox1c1ty of N-[B-(p-annno- 1956, Ser. No. 621,986 phenyl)ethyl] -4-phenyl-4-carboethoxypiperidine is less than one-tenth that of meperidine. 6 Clams (CL 260-2943) It is a preferred and unobvious embodiment of this invention that N-[/3(p-aminophenyl)ethyl]-4-phenyl-4- carboethoxypiperidine, its acyl derivatives, and salts, are effective upon being administered by the oral route, and PiPeridine defivatives- More Particularly, it relates that their analgesic activity when so administered is, in N [5 (P ph ny l yll 4 p y 4 fact, equal to their activity when administered parenteralethoxypiperidine, its monoacyl derivatives, and salts 1 h rally-administered N- 1 thereof, new compounds which possess superior analgesic ethyl]-4-phenyl-4-carboethoxypiperidine possesse activity, and to the process of p p n' g these n a parable analgesic activity to parenterally administered gesic ubstances Starting Wi h 4-phenyl-4-carboethoxymeperidine, even when the former is administered at a piperidine. dosage level of one-fourth that of the latter.

This application is a division of copending application The N-[B-(p-aminophenyl)ethyl]-4-phenyl-4-carboeth- Serial No. 511,414, filed May 26, 1955. oxypiperidine, its monoacyl derivatives, and salts thereof, The N [,6 (p aminophenyl)ethyl] 4 phenyl 4 can be prepared by reactions which may be chemically carboethoxypiperidine, its monoacyl derivatives, and salts represented as follows:

This invention is concerned generally with novel piperidine compounds and with processes for preparing these CuHs COOCzHs Compound 1 Compound 2 Compound 3 Acylating @111: lHA

COOCzHs COOC2H5 Compound 4 Compound 5 thereof, subject of the present invention may be chemiwherein X is halogen, R is acyl, R is hydrogen or an cally represented by the following structural formula: acyl radical, HA is an acid, I: equals 1 when R is acyl,

and n equals 1 or 2 when R is hydrogen.

The reactions indicated hereinabove are conducted as Q follows: 4-phenyl-4-carboethoxy-piperidine carbonate, or COOOzHt other acid salt, (Compound 2 hereinabove) is reacted wherein R is a hydrogen or an acyl radical, HA is an acid, with a l -(pp yn y halide (Compound n equals 1 when R is acyl, and n equals 1 or 2 when R thereby forming -[fi (P- P Y Y P y i h d 4-carboethoxypiperidine (Compound 3); the latter com- The chemical relationship of N-[fi-(p-aminophenynpound is reacted with an acid to produce the correspondethyl]-4-phenyl-4-carboethoxypiperidine to the welling Salt of the -[B-(pp y hyl]- -pheny1-4- known analgesic, meperidine, is clear from a comparison carboethoxypiperidine (Compound 5 Where R is y of the foregoing formula with the structural formula of alternatively the -lfi-(pp y y l- 'di hi h i as f ll phenyl-4-carboethoxypiperidine is reacted with an acyl- C6H5 ating agent, preferably a lower alkanoic anhydride, thereby producing the corresponding N-[B-(p-acylaminophenyl ethyl] -4-phenyl-4-carboethoxypiperidine (Compound 4) which is converted by reaction with an acid to the Although meperidine has been Widely used as an analcorresponding salt of N I 'P Y P Y gesic, its toxicity has been a disadvantage in many in- Pheny1'4Carboethoxyplpendme (Compound 5 Where R stances. A large number of N-substituted analogues of 1s acynmeperidine have been prepared heretofore in the hope reactlon between the 4jphenyl'4'carboethoxyof obtaining a compound having comparable analgesic plpfandme carbonate, Q OPheT acldfialtr and the B-(P- activity to meperidine and reduced toxicity, but none of t p yb yl halide 1S c n niently ctm uctcd by the compounds thus prepared have ofiered a satisfactory heatlng the reactants together In a medium is substitute for meperidine. There was no reason to expect Substantially inert under the e ction Conditions and from this prior work that this line of investigation would Which is a solvent for the reactants. We ordinarily lead to an improved analgesic of the meperidine type, utilize, as the liquid medium, a lower alkanol such as CHr-N ethanol, and prefer to conduct the reaction by heating the reactants together in said alkanol solvent underrefiux in the presence of an alkali metal bicarbonate such as sodium bicarbonate. As the B-(p-aminophenyDet-hyl halide starting material, we can utilize the chloride, bromide or iodide but we ordinarily prefer to employ an acid salt of either ,B-(p-aminophenybethyl chloride or fl-(p-aminophenyDethyl bromide. Utilizing these preferred reactants and under the preferred reaction conditions, the reaction is ordinarily substantially complete in about one to two days. The N-'[fl-(p-aminophenyl)- ethyl]-4-phenyl-4-carboethoxypiperidine thus formed is conveniently recovered from the reaction mixture by removing the inorganic saltsby filtration, and evaporating the resulting alcoholic solution to dryness in vacuo. The residual gummy mass is triturated with water, the water is decanted, and the residual material is dried in vacuo to give N-[fi-(p-aminophenyl)ethyl]4-phenyl-4-carboethoxypiperidine base.

The N 8 (p-aminophenyl)ethyl]4-phenyl-4-carboet-hoxypiperidine base may then be reacted with an acylating agent as for example benzoic'anhydride, a lower alkanoic acid anhydride such as acetic anhydride, propionic anhydride, and the like, thereby monoacylating the primary amino substituent of the N-[fi-(p-aminophenyD- ethyl]-4-phenyl-4-carboethoxypiperidine to form the corresponding N-[fi-(p-acylaminophenyl)ethyl]-4-phenyl-4- carboethoxypiperidine such as N-[fl-(p-acetylaminophem yl) ethyl -4-phenyl-4-carboethoxypiperidine, N- {3- (p-propionylaminophenyl ethyl] -4 -phenyl-4-carboethoxypip eridine, N [,8 (p-benzoylaminophenyl)ethyl]-4phenyl-4- carboethoxypiperidine, and the like. The reaction between the acyl anhydride and the N-[fl-(p-aminophenyD- ethyl]-4-phenyl-4-carboethoxypiperidine is ordinarily carried out in solution in an inert solvent under substantially anhydrous conditions. For example, when utilizing a lower alkauoic anhydride-such as acetic anhydride, the reaction is conveniently carried out in glacial acetic acid medium. The acylation reaction can be carried out at room temperature or at an elevated temperature of about 100 C. under which conditions the reaction is ordinarily complete in about one hour. The N-[fi-(p-acylaminophenyl)ethyl]-4-phenyl4-carboethoxypiperidine is conveniently recovered from the reaction mixture by diluting the latter with water and neutralizing the, acidic components with sodium carbonate whereupon the acylated product precipitates as a guru which is readily isolated from the aqueous. layer by decantation. This gummy material is further, purified-by washing with water and drying in vacuo.

The conversion of N-[fl-(p-aminophenyl)ethyl]4- phenyl-4-carboethoxypiperidine, or its monoacyl derivatives, the N-[fi-(p-acylaminophenyl)ethyl]4-phenyl-4- carboethoxy-piperidine, to thecorresponding mono and di salts. is. ordinarily conductedby reacting the N-[B-(paminophenyl ethyl] -4-phenyl-4-carboethoxypiperidine or the N [[3 (p-acylaminophenyl)ethyl]4-phenyl-4-carboethoxypiperidine, under substantially anhydrous conditions, with an acidas, for example, hydrogen chloride, hydrogen bromide, sulfuric acid, and the like. This saltformingreaction is conveniently carried out in a medium comprising a .lower alkanol, such as ethanol, methanol, propanol, and the like. Upon; diluting the'alkanol reactioumedium withethenthere precipitates the corresponding salt of the Ne[B(p-arninophenyl)ethyl]-4- phenyl-4-carboethoxypiperidine, or the. salt of N-[ S-(pacylaminophenyDethyl] 4 phenyl 4-carboethoxypi-per idine, such as N-[fi-(p-aminophenyDethyl]-4-phenyl-4- carboethoxypiperidine dihydrochloride, N-[fi-(p-aminophenyl)ethyl]-4 -phenyl-4-carboethoxypiperidine sulfate, N [(3 (p aminophenyl)ethyl]-4-phenyl-4-carboethoxypiperidine dihydrobromide, N-[B-(p-acetylaminophenyl)- ethyl]4 -phenyl-4-carboethoxypiperidine hydrochloride, N 3 (p acetylaminophenyDethyl]-4-phenyl-4-carboethoxyp iperidine. ulfat N=[fi:(R-P Pi 1 Y a P n1 4 yl)ethyl]-4-phenyl-4-carboethoxypiperidine hydrochloride, N [,8 (p-benzoylaminophenyl)ethyl]4-phenyl-4-carboethoxypiperidine hydrochloride, N-[fi-(p-acetylaminophenyl)ethyl] 4 phenyl-4-carboethoxypiperidine hydrobromide, and the like. The salt thus formed is recovered from the alcoholic slurry by filtration or centrifugation.

The following examples illustrate methods of carrying out the present invention, but it is to be understood that these examples are given for purposes of illustration and not of limitation.

Example 1 decantation with an additional 50 cc. of water, and then dried in vacuo to give N-[fl-(p-arniuophenyhethyl]-4 phenyl-4-carboethoxypiperidine.

The N [B (p-aminophenyl)ethyl]4-phenyl-4-carboethoxypiperidine is dissolved in 50 cc. of hot anhydrous.

ethanol, an excess. (about 20 cc.) of 20% alcoholic hydrochloric acid solution is added; upon scratching the; side of the container crystals form. One hundred cubic-,-

centimeters of ether are then added to the mixture, the

ethereal mixture is cooled, and the crystalline material,

which precipitates is recovered by filtration, washed with ether, and dried to give 12.7 g. of N-[B-(p-aminophenyhethyl]-4-phenyl-4-carboethoxypiperidine dihydrochloride which can be further purified by recrystallization from ethanol or methanol to give substantially pure material; M.P. 275-277 C. Calcd. for C H O N 2HCl: C, 62.12; H, 7.11; N. 6.59; Cl, 16.67. Found: C, 61.75; H, 6.90; N, 6.48; Cl, 16.60.

The fl-(p-aminophenyDethyl chloride hydrochloride used as starting material in theforegoing example may be prepared as follows: A mixture of 111 g. acetic anhydride and 66 g. of acetic acid is cooled to 0 C., 69 g. of fuming nitric acid is added slowly, and the mixture is cooled to -5 C. To the cold mixture thus obtained is added dropwise with stirring 101 g; fiphenylethyl bromide over a period of about two hours while maintaining the temperature of the mixture between about 10 and 0 C. The nitration mixture is stirred for an additional two-three hours at a temperature below 0 C., and the reaction mixture is poured into a suspension of 145 g. sodium carbonate in 1100 cc. ice water. The yellow product is extracted from the aqueous mixture with benzene, the benzene extract is washed with excess sodium bicarbonate solution, then with water, and then dried over magnesium sulfate. The benzene is evaporated from the resulting solution in vacuo, and the residual material is crystallized from petroleum ether to give about 55 g. of ,B-(p-nitio phenyl)ethyl bromide; M.P. 65-67 C. To a solution containing 172 g. stannous chloride in 430 cc. concentrated aqueous hydrochloric acid is added portionwise with shaking 43 g. of fi-(p-nitrophenyhethyl bromide over a period of about 45 minutes. The resulting mixtureis warmed for an additional 45 minutes on a steam bath, and the aqueous solution is decanted from some oily material. The resulting solution .iscooled, 750 cc. of a 30% aqueous sodium hydroxide solution is added, and the resulting cold aqueous alkaline solution is extracted with 400 cc. of ether and then with two 200 cc. portions of ether. The combined ether extracts are washed with two 300 cc. portions of water and the washed ether solution is shaken with cc. of 3.5 N aqueous hydrochloric acid solution whereupon crystallization takes place immediately. The crystalline slurry is cooled to about 0 C., allowed to stand to complete crystallization, the slurry is filtered, and the crystals are washed with three 25 cc. por

tions of ice water and dried in vacuo to give about 30 g. of a mixture of B-( p-aminophenyl)ethy1 bromide hydrochloride and fi-(p-aminophenynethyl chloride hydrochloride.

Example 2 One gram of N-[fi-(p-aminophenyl)ethyl]-4-phenyl-4- carboethoxypiperidine dihydrochloride prepared as described in Example 1 hereinabove is dissolved in 25 cc. of water, excess sodium hydroxide solution is added, and the aqueous alkaline mixture is extracted with two 50 cc. portions of ether. The ether extracts are combined, dried over magnesium sulfate, and evaporated to dryness in vacuo to give N-[fl-(p-aminophenyl)ethyl]-4-phenyl-4- carboethoxypiperidine base. This material is mixed with 2 cc. glacial acetic acid and 2 cc. of acetic anhydride, and the resulting mixture is heated on the steam bath for a period of about one hour, and then allowed to stand overnight at room temperature. The reaction mixture is diluted with 25 cc. of water, an excess of sodium bicarbonate is added portionwise whereupon a gummy precipitate forms. The aqueous layer is decanted from this precipitate and the latter is washed by decantation with three 15 cc. portions of water, and dried in vacuo to give N [,8 (p acetylaminophenyl)ethyl] 4 phenyl 4 carboethoxypiperidine base.

The N- [,8- (p-acetylaminophenyl) ethyl] -4-phenyl-4-carboethoxypiperidine base is dissolved in 10 cc. of anhydrous ethanol, a trace of salt which forms is removed by filtration and to the filtered solution is added an excess (2 cc.) of 20% alcoholic hydrochloric acid solution. Crystallization occurs immediately, the crystalline slurry is cooled to C. and filtered, and the crystalline material is washed with four 3 cc. portions of cold anhydrous ethanol and dried to give about 0.5 g. of N-[fl-(p-acetylaminophenyl) ethyl] 4-phenyl-4-carboethoxypiperidine hydrochloride; M.P. 264-265 C.

Calcd. for C H O N .HCl: C, 66.88; H, 7.25; N, 6.50. Found: C, 67.18; H, 7.57; N, 6.39.

Example 3 To a solution of 1.8 g. (0.005 mole) of purified N [fi (p aminophenyl)ethyl] 4 phenyl carboethoxypiperidine in 10 cc. of anhydrous ethanol is added 8.2 cc. of 2.23% ethanolic hydrogen chloride (0.005 mole). The mixture is chilled at about 0 C. overnight. The crystals of N-[/8-(p-aminophenyl)ethyl]-4-phenyl-4- carboethoxypiperidine monohydrochloride thus obtained are filtered, washed with 3 cc. portions of ice-cold anhydrous ethanol and dried. 1.0 g. of product is obtained, M.P. 218-220 C.

Calcd. for C H O N HCl: C, 67.96; H, 7.54; N, 7.20. Found: C, 67.79; H, 7.23; N, 7.39.

The purified N-[B-(p-aminophenyl)ethyl]-4 phenyl-4- carboethoxypiperidine used as starting material in the foregoing example may be prepared as follows: g. of

the pure dihydrochloride salt obtained as described in Example 1 is dissolved in water and treated with an excess of aqueous sodium hydroxide solution. The liberated base is extracted into ethyl ether, and the other extracts dried over magnesium sulfate. Concentration of ether extracts to dryness in vacuo affords a residue of substantially pure N-[,B-(p-aminophenyl)ethyl]-4-phenyl-4-carboethoxypiperidine free base.

The new compounds obtained as described hereinabove have been referred to as substituted piperidines, alternatively they may be considered as derivatives if isonipecotic acid. Thus N-[B-(p-aminophenyhethyl]-4-phenyl-4-carboethoxypiperidine may be named as ethyl 1-(4-aminophenylethyl)-4-phenyl isonipecotate.

Various changes and modifications may be made in carrying out the present invention without departing from the spirit and scope thereof. Insofar as these changes and modifications are within the purview of the annexed claims, they are to be considered as part of our invention.

We claim:

1. A compound selected from the group which consists of N-[B-(p-aminophenyDethyl]-4-phenyl-4-carboethoxypiperidine compounds having the formula:

CuHa

COOCnH References Cited in the file of this patent UNITED STATES PATENTS 2,748,140 Schmidle et a1. May 29, 1956 2,784,192 Schmidle et a1. Mar. 5, 1957 2,792,399 Eckenstam et a1 May 14, 1957 OTHER REFERENCES Merck Index, sixth ed., pp. 7 and 128 (1952). 

1. A COMPOUND SELECTED FROM THE GROUP WHICH CONSISTS OF N-(B-(P-AMINOPHENYL)ETHYL)-4-PHENYL-4-CARBOETHOXYPIPERIDINE COMPOUNDS HAVING THE FORMULA: 